In recent years, the functionality offered by mobile telecommunications systems has been expanded from pure (circuit-switched) voice communication to a variety of services in addition to voice calls. Many of these additional services employ packet-switched data communication between a server and a mobile terminal, or between two mobile terminals, over the mobile telecommunications network and associated wide area networks such as the Internet. For instance, the 3G/UMTS (3rd Generation/Universal Mobile Telecommunications System) architecture involves packet-based communication in accordance with the High Speed Packet Access (HSPA) protocol set, including High Speed Downlink Packet Access (HSDPA) for downlink communication and High Speed Uplink Packet Access (HSUPA), also known as Enhanced Uplink (EUL), for uplink communication. These protocols are defined in the 3rd Generation Partnership Project (3GPP) standards.
In any packet-switched communication system, problems like packet losses or congestion between competing data flows can occur at various locations in the system. Data flow control is therefore provided at several levels in the protocol architecture. For instance, in the 3G/UMTS (3rd Generation/Universal Mobile Telecommunications System) architecture, the Transmission Control Protocol (TCP) may be applied on an upper level between a TCP server and an end-user application in a mobile terminal (user equipment, UE). Radio Link Control (RLC) is applied between a Serving Radio Network Controller (SRNC) and a UE, whereas HSPA Flow Control (FC) is applied to HSPA traffic flows over the Transport Network (TN; Iub) between an SRNC and a Radio Base Station (RBS; Node B)).
For downlink traffic, i.e. HSDPA, the control of radio frame scheduling resides in the Node B:s rather than the SRNC:s. While fix capacity (e.g. 64-384 kbps) can be reserved by way of admission control for traditional Dedicated Channel (DCH) traffic in the radio access network, for HSDPA, per-flow bandwidth reservation is not efficient. This is mainly because the bit-rates can vary considerably between different kinds of traffic flows. Instead, HSDPA flows use a best effort-type of connection over the transport network. When bandwidth reservation is not used, congestion situations can occur both in the transport network and in the air interface. TCP cannot efficiently resolve a congestion situation in the radio access network, because lower layer retransmissions hide the congestion situations from TCP. It is a common scenario that the throughput is limited by the capacity available on the Iub transport network links and not by the capacity of the air interface, and it is important to maintain high efficiency on these high cost links. Thus, HSDPA Flow Control (FC) has been introduced to control the data transfer between the SRNC and Node B over the transport network. While on the air interface it is the task of the air interface scheduler to share the bandwidth among the flows, on Iub it is the task of the FC to provide fair bandwidth sharing among the flows of the same priority.
Similarly, for uplink traffic, i.e. EUL, the uplink radio scheduling resides in the Node B. The EUL traffic has similar properties to that of HSDPA, though it can reach somewhat lower bitrates. For EUL, too, the transport network is a potential bottleneck, and therefore EUL Flow Control is provided.
The likelihood for transport network bottlenecks to occur is increased by the fact that in most instances of cellular systems, the transport network is expensive and is therefore not deployed to a degree where all peak bit-rates fit at the same time. The transport network is often rolled out in a pace, which corresponds to the average traffic growth over time.
Both HSDPA FC and EUL FC handle such occurring transport network bottlenecks by way of rate-based per-flow flow control. Each flow is controlled in an identical way. Rate-based flow control means that the bit-rate of each contending traffic flow is regulated by the FC algorithm, and is used because the lack of sequence numbering and retransmission in the 3GPP standard does not allow a window-based flow control, like TCP. While RLC in the 3G system provides sequence numbering and retransmission functionality, the RLC protocol layer is not terminated in Node B and is, therefore, difficult to use for FC purposes.
The FC algorithms operate according to the Additive Increase Multiplicative Decrease (AIMD) principle, which is well known as such and which ensures convergence to fair bandwidth share among contending traffic flows which are subjected to the same transport network bottleneck (having the same Transport Network layer QoS (Quality of Service) class, and sharing same path in the transport network). QoS differentiation is intended to be solved by Transport Network layer QoS differentiation.
The present inventors have realized that, in situations when the transport network is a bottleneck, it would be beneficial to be able to differentiate between different type of subscriptions, e.g. such that users with a higher-ranked subscription are favored in terms of QoS (Quality of Service) over users with a lower-ranked subscription for the same bottleneck in the transport network. The present inventors have also realized that Transport Network layer QoS (Quality of Service) differentiation as such may not be a sufficient solution.
Therefore, there is room for improvements with respect to these problems.